This invention relates to a hybrid integrated circuit device and, more particularly, to a hybrid integrated circuit device in which a chip resistor is disposed on a thick film circuit board and electrically connected thereto by a solder.
FIG. 9 is a fragmental plan view of a known hybrid integrated circuit device and FIG. 10 is a sectional view taken along line X--X of FIG. 9. As illustrated in FIGS. 9 and 10, a chip resistor 3 comprises an electrically insulating substrate 3a made, for example, of ceramic, two electrodes 5 disposed at opposite ends of the electrically insulating substrate 3a and a resistor element 4 disposed on the top surface of the electrically insulating substrate 3a and electrically connected to the electrodes 5. The resistor element 4 is made of a resistance material having a small electrical resistance of the order of m.OMEGA..
As seen from FIGS. 9 and 10, two electrical conductors 2 are disposed on a thick film circuit board 1 so that each can be contacted to the electrodes 5 of the chip resistor 3. The chip resistor 3 is mounted on the circuit board 1 and the electrodes 5 of the chip resistor 3 are electrically connected to the electrical conductors 2 by means of solder 6.
In the known hybrid integrated circuit device as described above, the chip resistor 3 having the resistor element 4 is electrically connected to the electrical conductors 2 which disposed on the circuit board 1 through the solder 6 so as to form a resistance on the circuit board 1 as well as through the direct contact surface of the electrode 5. That is, electrical current which flows between the electrical conductor 2 and the electrode 5 flows through two routes, one including the solder 6 and the other not including the solder 6. Therefore, the total resistance between the conductors 2 is determined by the resistances of the two routes connected in parallel, one of which is through the solder 6 and the electrode 5 and the other of which is only through the electrode 5.
In the known hybrid integrated circuit device as described above, when undesirable stresses due to thermal stresses, applied to the connecting portions between the solder 6 and the chip resistor 3, shearing, tension and/or compression can occur and, further, cracks 7 might happen to be generated as illustrated in FIG. 11. When cracks 7 occur between the solder 6 and the electrodes 5, one of the current routes which extends from the electrical conductor 2 to the electrode 5 through the solder 6 becomes almost interrupted. Therefore, the resistance between the electrical conductor 2 and the resistor element 4 becomes merely that of the electrode 5 which is in direct contact with the conductor 2 and the total resistance between the conductors 2 is also changed, resulting in unreliable electrical characteristics. Further, as the resistance of the resistor element 4 is very small, the cracks 7 have a significant harmful influence upon the total resistance.